1. Field of the Invention
The present invention relates to a particle beam irradiation system, and more particularly to a particle beam irradiation system for irradiating a charged particle beam, such as a proton or carbon ion beam, to an affected part of the body for treatment.
2. Description of the Related Art
There is known a therapy method of irradiating a charged particle beam (ion beam), such as a proton or carbon ion beam, to an affected part, e.g., a cancer, in the body of a patient. A particle beam irradiation system for use with such a therapy method comprises a charged particle beam generator, a beam line, and a treatment room. The charged particle beam accelerated by an accelerator in the charged particle beam generator reaches an irradiation device in the treatment room through the beam line, and it is irradiated to the affected part of the patient body from the irradiation device after being scanned by a scanning magnet disposed in the irradiation device. In that type irradiation system, it has also hitherto been known to stop output of the charged particle beam from the irradiation device, to change (scan) an exposure position (spot) of the charged particle beam by controlling the scanning magnet in the state where the output of the charged particle beam is stopped, and after the change of the exposure position, to start the output of the charged particle beam again from the irradiation device (see, e.g., Patent Document 1; Japanese Patent No. 2833602 (FIG. 1, etc.))